It takes time but usually the intensity and duration of the activity determine how long the effect will last. The effect will not last a week but the literature states about 24-48 hours.
It would probably take a non exercising person about 2-3 months of steady state exercise to reach that level of high level metabolic rate (Fat burning index).
So then you have been able to accomplish this or are you merely passing on what you have read elsewhere? I do find that the body generates a lot of heat for about 12 hours after strenuous activity.
As a former marathoner and former Marine, I would run the equivalent of 5 miles a day. When I compare my research background with exercise physiology principles and concepts, the only way is to increase BMR is to increase intensity (The main variable) with a consistant frequency (3-4 times a week). WIth research, one learns (Or tries to) to apply the best strategy to get the best results.
As a big belly man (To much Carib beer), walking was not sufficent to increase BMR and I hated weightlifting so I had to either start lifting or do more distance.
Both worked for awhile but as sarcopenia began to creep in, I decreased the distance and started more weight lifting to increase muscle power and help the type 1 and IIb fibers.
What you can do is admirable but 1 session generating 12 hours of heat seems implausible unless one is gungho about weight lifting and the session last 2-3 hours at that one session. People would pay a lot just to learn how to do that so all power to you!
Why base metabolism varies with mass. A multidisciplinary team of researchers has managed to solve a puzzle that had bewildered biologists for over a century: how and why an organism’s base metabolism varies depending on its mass. Base metabolism is the minimum energy that an organism consumes to stay alive. Source 5t.